Japanese currency intervention, how does disaster promote a strong currency?

After the catastrophic earthquake, the tsunami, and the nuclear-reactor scares, the Japanese currency ironically strengthened quite sharply. In response, the Bank of Japan and other major central banks last week launched a coordinated “intervention” into the currency markets in order to intentionally weaken the yen.
In this article I’ll explain why the yen strengthened in the first place, and the problems with the central-bank maneuvers……………………………………….Full Article: Source